Data on the enteric methane emissions of individual cows are useful not just in assisting management decisions and calculating herd inventories but also as inputs for animal genetic evaluations. Data generation for many animal characteristics, including enteric methane emissions, can be expensive and time consuming, so being able to extract as much information as possible from available samples or data sources is worthy of investigation. The objective of the present study was to attempt to predict individual cow methane emissions from the information contained within milk samples, specifically the spectrum of light transmittance across different wavelengths of the mid-infrared (MIR) region of the electromagnetic spectrum. A total of 93,888 individual spot measures of methane (i.e., individual samples of an animal's breath when using the GreenFeed technology) from 384 lactations on 277 grazing dairy cows were collapsed into weekly averages expressed as grams per day; each weekly average coincided with a MIR spectral analysis of a morning or evening individual cow milk sample. Associations between the spectra and enteric methane measures were performed separately using partial least squares regression or neural networks with different tuning parameters evaluated. Several alternative definitions of the enteric methane phenotype (i.e., average enteric methane in the 6 d preceding or 6 d following taking the milk sample or the average of the 6 d before and after the milk sample, all of which also included the enteric methane emitted on the day of milk sampling), the candidate model features (e.g., milk yield, milk composition, and milk MIR) as well as validation strategy (i.e., cross-validation or leave-one-experimental treatment-out) were evaluated. Irrespective of the validation method, the prediction accuracy was best when the average of the milk MIR from the morning and evening milk sample was used and the prediction model was developed using neural networks; concurrently including milk yield and days in milk in the prediction model generated superior predictions relative to just the spectral information alone. Furthermore, prediction accuracy was best when the enteric methane phenotype was the average of at least 20 methane spot measures across a 6-d period flanking each side of the milk sample with associated spectral data. Based on the strategy that achieved the best accuracy of prediction, the correlation between the actual and predicted daily methane emissions when based on 4-fold cross-validation varied per validation stratum from 0.68 to 0.75; the corresponding range when validated on each of the 8 different experimental treatments focusing on alternative pasture grazing systems represented in the dataset varied from 0.55 to 0.71. The root mean square error of prediction across the 4-folds of cross-validation was 37.46 g/d, whereas the root mean square error averaged across all folds of leave-one-treatment-out was 37.50 g/d. Results suggest that even with the likely measurement errors contained within the MIR spectrum and gold standard enteric methane phenotype, enteric methane can be reasonably well predicted from the infrared spectrum of milk samples. What is yet to be established, however, is whether (a) genetic variation exists in this predicted enteric methane phenotype and (b) selection on estimates of genetic merit for this phenotype translate to actual phenotypic differences in enteric methane emissions.

Similar to all dairy systems internationally, pasture-based dairy systems are under increasing pressure to reduce their greenhouse gas (GHG) emissions. Ireland and New Zealand are 2 countries operating predominantly pasture-based dairy production systems where enteric CH4 contributes 23% and 36% of total national emissions, respectively. Ireland currently has a national commitment to reduce 51% of total GHG emissions by 2030 and 25% from agriculture by 2030, as well as striving to achieve climate neutrality by 2050. New Zealand's national commitment is to reduce 10% of methane emissions by 2030 and between 24% and 47% reduction in methane emissions by 2050. To achieve these reductions, factors that affect enteric methane (CH4) production in a pasture-based system need to be investigated. The objective of this study was to assess the relationship between enteric CH4 and other animal traits (feed intake, metabolic liveweight, energy corrected milk yield, milk urea concentration and body condition score) in a grazing dairy system. Enteric CH4 emissions were measured on 45 late lactation (213.8 ± 29 d after calving) grazing Holstein-Friesian and Holstein-Friesian × Jersey crossbred cows (Lactation number 3.01 ± 1.65, 538.64 ± 59.37 kg live weight, and 3.14 ± 0.26 body condition score) using GreenFeed monitoring equipment for 10 weeks. There was a training period for the cows to use the GreenFeed of 3 weeks before the 10 week study period. The average enteric CH4 produced in the study was 352 g ± 45.7 g per day with an animal to animal coefficient of variation of 13%. Dry matter intake averaged 16.6 kg ± 2.23 kg per day, while milk solids (fat plus protein) averaged 1.62 kg ± 0.29 kg per day. A multiple linear regression model indicated that each one unit increase in energy corrected milk yield, metabolic liveweight and milk urea concentration, resulted in an increase in enteric CH4 production per day by 3.91g, 1.74 g and 1.38 g, respectively. While each one unit increase in body condition score resulted in a decrease in 39.03 g CH4 produced per day. When combined, these factors explained 47% of the variation in CH4 production, indicating that there is a large proportion of variation not included in the model. The repeatability of the CH4 measurements was 0.66 indicating that cows are relatively consistently exhibiting the same level of CH4 throughout the study. Therefore, enteric CH4 production is suitable for phenotyping.

Early lactation is a critical period for dairy cows, as energy requirements rapidly increase with the onset of lactation; however, early-lactation DMI in pasture-based systems are under measured. The objectives of this study were (1) to measure and profile total DMI (TDMI) and animal performance of dairy cows during early lactation in a pasture-based system, (2) to investigate early-lactation energy balance in pasture-based systems, and (3) to examine production efficiencies, including TDMI and milk solids production per 100 kg of BW. Eighty spring-calving dairy cows were allocated to a grazing group as they calved over a 2-yr period (2021 and 2022). Cows were offered a daily herbage allowance to achieve a postgrazing sward height of 4 cm, with silage supplementation when necessary due to inclement weather. Total DMI was measured using the n-alkane technique over a 12-wk period from February 1, 2021, to April 23, 2022. Total DMI and daily milk yield were significantly affected by parity with both variables being greatest for third-parity animals (17.7 kg of DM and 26.3 kg/cow per day, respectively), lowest for first parity (13.2 kg of DM and 19.6 kg/cow per day, respectively) and intermediate for second-parity animals (16.8 kg of DM and 24.1 kg/cow per day, respectively). Peak TDMI was reached on wk 10 for first-parity animals (14.6 kg of DM), wk 11 for second parity animals (19.3 kg of DM) and wk 12 for third-parity animals (19.9 kg of DM). Parity also had a significant effect on unité fouragère lait (UFL; feed units for milk) feed balance as first-parity animals experienced a greater degree of negative energy balance (-3.2 UFL) compared with second- and third-parity animals (-2.3 UFL). Breed and parity had an effect on production efficiencies during the first 12 wk of lactation as Jersey × Holstein Friesian cows had greater TDMI/100 kg of BW and milk solids/100 kg of BW compared with Holstein Friesian cows.

Maximising herbage yield while reducing nitrogen (N) fertiliser input, particularly in spring, is essential to ensure environmental and economic sustainability on grassland farms. A plot experiment was conducted over 2 yr, comparing three different spring N application rates of 30 (30N), 60 (60N) and 90 (90N) kg N/ha using three different spring application strategies: 0:100 (S1), 50:50 (S2) or a 33:66 (S3) split across February and March, respectively. Half of the plots also received phosphorus (P) fertiliser with the first application of N at a rate of 13 kg P/ha. Nitrogen fertiliser application for the remainder of the year (April-September) was the same for all plots (23 kg N/ha/ application). Both spring and cumulative herbage yields were significantly affected (P < 0.05) by N application rate; 90N had the greatest spring and cumulative herbage yield compared to 30N and 60N (10,925, 9,834 and 10,499 kg DM/ha, respectively); however, N response reduced as N application rate increased. Nitrogen application strategy had a significant effect (P < 0.05) on spring herbage yield, with S1 significantly lower than S2 and S3. Applying 13 kg P/ha in spring increased herbage yield at defoliations 2 (23 April) and 3 (15 May) (+133 and 56 kg DM/ha, respectively), relative to no application of P fertiliser, as well as increasing cumulative herbage yield (+241 kg DM/ ha). The results of the current study indicate that N should be applied in early February and the strategic application of N and P during spring can increase spring and cumulative herbage yield.

Although 3-nitroxypropanol (3-NOP) has been proven to reduce enteric methane (CH4) by similar to 30% in indoor systems of dairying when the additive is mixed throughout a TMR, very limited research has been done to date in grazing systems in which the most convenient method of additive supplementation is at milking twice daily. To investigate the effect of twice daily 3-NOP supplementation on enteric CH4 emissions, a 12-wk study was undertaken in which treatment cows (n = 26) were supplemented with 3-NOP (80 mg/kg DMI) twice daily at morning and evening milking, and control cows (n = 26) received no additive supplementation. Enteric CH4, hydrogen (H-2) and carbon dioxide (CO2) were measured using GreenFeed units, and milk production, BW, BCS, and DMI were monitored to determine the effect of 3-NOP supplementation on productivity. No significant effect was observed for 3-NOP supplementation on any of the aforementioned parameters with the exception of CH4 and H-2 production, respectively. Cows supplemented with 3-NOP produced 1.6-fold more H-2 (P < 0.001) across a 24-h period, with reductions in CH4 production of 28.5% recorded in the 3 h after additive consumption (P < 0.001), however, levels of CH4 production returned to that of the control group thereafter. When CH4 production was considered across the entire 24-h period, the cows offered 3-NOP produced similar to 5% less CH4 than the control (P < 0.050). Future research should focus on methods to increase the efficacy of the additive throughout the day which would include the deployment of a slow-release form or an out-of-parlor feeding system that allows animals consume the product at additional time points.

Little data are currently available on either the dry matter (DM) production of perennial ryegrass (PRG) swards as they age beyond 5 yr (i.e. permanent pasture) or the performance of PRG varieties on commercial grassland farms. Previous work has generally assumed a connection between DM production and ground score (GS) and this link has been used as a proxy for variety persistence. The evolution of technology in the form of PastureBase Ireland has led to agronomic data of individual paddocks being made available for analysis over multiple years which has allowed the long-term assessment of varieties sown as monocultures on commercial farms. This technology allowed for the inclusion of eight PRG varieties sown in 649 paddocks across 101 farms in Ireland in the current analysis. The results show little association between GS and variety DM production as varieties age to 7 yr. Dry matter production of 1- to 4-yr-old swards appeared to provide a strong indication of variety DM production in years 5–7 post-sowing (r = 0.72, P < 0.05). The interaction of variety and sward age was not associated with DM production. Generally, varieties which produced the most DM in younger swards also produced the most DM in permanent pasture swards. Over longer-term periods these variety differences can manifest into large differences in DM produced and consumed on farm. The current analysis suggests that the long-term production benefits of utilising improved PRG varieties in pasture reseeding may be underestimated.

The increased average Irish dairy herd size in a post-quota environment has put heightened pressure on grazing infrastructure. In a rotational grazing system, grazing infrastructure consists of the paddock system, which delineates the grazing areas into appropriately sized grazing parcels, and the roadway network, which connects these paddocks to the milking parlor. Where herd size has increased without corresponding adaptations to the infrastructure, farm management and roadway network performance has been affected. The links between suboptimal grazing infrastructure and roadway network efficiency are poorly understood and not widely documented. The aims of this study were to (1) analyze the effect of herd expansion and paddock size on pasture allocations per paddock, (2) identify the factors that affect the total distance walked per year, and (3) create a metric to compare the efficiency of roadway networks across farms of varying grazing platforms. A sample population of 135 Irish dairy farms with a median herd size of 150 cows was used for this analysis. Herds were split into the following 5 categories: <100 cows, 100 to 149 cows, 150 to 199 cows, 200 to 249 cows, and ≥250 cows. Herds with ≥250 cows had a greater number of paddocks per farm and rotated around the grazing paddocks more frequently, with 46% of paddocks only suitable for 12 h allocations relative to herd size, compared with just 10% to 27% of paddocks for herds with <100 cows to herds with 200–249 cows. When predicting the total distance walked per year on each study farm, the mean distance from a paddock to the milking parlor was the strongest indicator (R2 = 0.8247). Other metrics, such as herd size, have failed to account for the location of the milking parlor relative to the grazing platform. The creation of the relative mean distance from a paddock to milking parlor (RMDMP) metric allowed the calculation of a farm's roadway network efficiency for moving the herd between paddocks and the milking parlor. The analyzed farms increased their efficiency in terms of RMDMP (0.34–40.74%) as they increased herd size post quota. However, the position of new additional paddocks relative to the milking parlor substantially affected their RMDMP.

AbstractIn pasture-based dairy production systems, identifying the appropriate stocking rate (SR; cows/ha) based on the farm grass growth is a key strategic decision for driving the overall farm business. This paper investigates a number of scenarios examining the effects of SR (2–3 cows/ha (0.25 unit changes)), annual nitrogen (N) fertilizer application rates (0–300 kg N/ha (50 kg/ha unit changes)), soil type (heavy and a free-draining soil) and agroclimate location ((south and northeast of Ireland) across 16 years) on pasture growth and forage self-sufficiency using the pasture-based herd dynamic milk model merged with the Moorepark St Gilles grass growth model. The modelled outputs were grass growth, grass dry matter intake, silage harvested and offered, overall farm forage self-sufficiency and N surplus. The model outputs calculated that annual grass yield increased from 9436 kg DM/ha/year when 0 kg N/ha/year was applied to 14 996 kg DM/ha/year when 300 kg N/ha/year were applied, with an average N response of 18.4 kg DM/kg N applied (range of 9.9–27.7 kg DM/kg N applied). Systems stocked at 2.5 cows/ha and applying 250–300 kg N fertilizer/ha/year were self-sufficient for forage. As N input was reduced from 250 kg N/ha/year, farm forage self-sufficiency declined, as did farm N surplus. The results showed that a reduction in N fertilizer application of 50 kg/ha/year will require a reduction in an SR of 0.18 cows/ha to maintain self-sufficiency (R2 = 0.90).

Little information is available on the phenotypic performance of perennial ryegrass varieties when exposed to grazing conditions on commercial grassland farms. Grass varieties are classically evaluated in mechanically defoliated plot systems which, although designed to mimic grazing conditions, do not fully capture the range of stresses or interactions that a sward is subjected to under commercial settings or over any period longer than 4 years. The evolution of technology in the form of PastureBase Ireland has led to agronomic data of individual paddocks being made available for analysis over multiple years. Data used in the current study consisted of dry matter (DM) production and ground score data across a 7-year period from ten perennial ryegrass varieties grown as monocultures in 559 paddocks on 98 commercial farms. The results demonstrated how perennial ryegrass variety is associated with a range of agronomic performance traits on commercial farms; including total and seasonal DM production, grazing DM production and number of grazing events. Varieties with the highest total DM production also had the highest spring and mid-season DM production; autumn DM production was associated with the interaction between variety and year. The highest producing variety in the study, AberGain, produced 1342 kg DM/ha/year more than the mean of all other varieties. Variety differences manifested themselves as swards aged, with some varieties increasing in total DM production while others reduced in total DM production. The current work provides a basis for the consideration of on-farm variety assessment in the composition of future variety evaluation protocols.

Altering autumn management affects the herbage mass available in spring. An experiment was established to determine the effect of five autumn closing dates (CDs) on herbage production, herbage quality, leaf, stem and dead proportions and tiller density over winter. In the study 50% of the herbage available in spring was accounted for by autumn CD. Each 1 d extra a sward was closed from 25 September to 9 December increased herbage mass by 16 kg DM/ha in spring. Swards closed earlier (25 September–26 October) had consistently higher herbage masses in spring (1,301 kg DM/ha) compared to swards closed later (11 November–9 December; 703 kg DM/ha). Later closed swards had greater herbage quality compared to earlier closed swards (organic matter digestibility = 852 and 825 g/kg DM, respectively) due to increased stem and dead material in the grazing horizon of earlier closed swards. There was no effect of autumn CD on sward quality in the subsequent defoliation in spring. However, following the initial spring grazing there was an effect of autumn CD on subsequent grass growth rates; swards closed in October had a lower growth rate (33 kg DM/ha per day) compared to swards closed in November and early December (49 kg DM/ha per day). Results indicate that earlier autumn closing is beneficial to meet high-feed demand in spring but can affect sward quality and growth rates in spring.

The importance of increased grass availability in the diet of the early lactation dairy cow in spring-calving pasture-based systems is widely reported. To combat the effect of low over winter growth rates, closing swards earlier in autumn can allow for greater accumulation of herbage for grazing in spring. The aim of this study was to identify the impact of three autumn closing treatments (varying closing rotation dates); (1) Early - September 25th to November 9th, (2) Normal - October 10th to November 24th and (3) Late - October 25th to December 9th, on late lactation milk production and early lactation milk production in the subsequent spring. The goal was to identify the optimum recommendations for autumn closing management to achieve increased milk production in spring resulting from increased grass availability, without compromising on animal performance in late lactation. There was no effect of autumn closing treatment on late lactation milk yield or milk solids yield. There was, however, a decline in milk protein concentration, associated with the diet change at housing of the early closed treatment (-1.6 g/kg milk) and normal treatment (-0.7 g/kg milk) in autumn compared with the late closed treatment (41.5 g/kg milk), as a result of the increased silage fed during this period (473.2, 345.8 and 163.8 kg DM/cow, respectively). Each one day increase in closing resulted in an extra 16 kg DM/ha in pre-grazing herbage mass on February 1st of the subsequent year (R-2 = = 0.502). The resulting increases in pre-grazing herbage mass contributed to increased daily herbage allowance (DHA; + 2.9 kg DM/cow) and total dry matter intake (+ 1.3 kg DM/cow) for the early treatment in spring compared with the normal and late closed treatment. Each 1 kg increase in DHA resulted in an increase of 0.38 kg milk/cow/day. A greater proportion of silage was required cumulatively on the early closed treatment (628 kg DM/cow) in contrast to the late closed treatment (419 kg DM/cow) between the autumn and spring period. However, the increased milk production associated with the increased grass availability in spring outweighed the cost associated with the increased silage requirement. Closing the farm early in autumn offers significant advantages in terms of higher DHA, increased dry matter intake and higher milk yields the following spring. Therefore, it is recommended the closing rotation should begin in late September and cease by mid-November, where there is a high demand for grass in early spring.

The objective of the current study was to explore differences in dry matter intake, intake capacity, production efficiency, energy balance, and grazing behavior, of 2 divergent genetic groups (GG) of lactating Holstein-Friesian, selected using the Irish Economic Breeding Index (EBI). The GG were evaluated across 3 spring calving pasture-based feeding treatments (FT) over 3 yr. The 2 divergent GG were (1) high EBI, representative of the top 5% nationally (elite), and (2) EBI representative of the national average (NA). In each year 90 elite and 45 NA cows were randomly allocated to 1 of 3 FT: control, lower grass allowance, and high concentrate. Although FT did affect animal performance, there were few notable incidences of GG × FT interaction. The elite cows expressed lower daily milk yield (-1 kg) compared with NA. Elite cows did, however, express higher daily concentrations of milk fat (+3.7 g/kg) and protein (+2.1 g/kg) compared with NA. Daily yield of milk solids and net energy of lactation (NEL) was similar for both GG. Body weight (BW) was greater for NA (+13 kg) compared with elite, whereas mean body condition score was greater (+0.14) for elite compared with NA. Intake did not differ significantly between GG. Intake capacity, expressed as total dry matter intake/100 kg of BW, was greater with elite compared with NA. Production efficiency expressed as yield of milk solids per 100 kg of BW was greater with elite compared with NA, although milk solids/total dry matter intake did not differ between GG. Expressed as NEL as a proportion of net energy intake minus net energy of maintenance (NEL/NEI - NEM) and NEI/milk solids kg, indicated a slight reduction in the utilization of ingested energy for milk production with elite compared with NA. This is, however, suggested as favorable as it manifested as a more positive energy balance with elite compared with NA and so is likely to enhance robustness, increase longevity, and increase overall lifetime efficiency. Noteworthy was a consistent numerical trend toward more intense grazing activity with elite compared with NA cows, exhibited in the numerically greater grazing time (+19 min) and total number of bites per day (+2,591).

AbstractThe importance of spring grass in the diet of early lactation dairy cows has been widely acknowledged. Numerous studies completed on a plot/paddock basis have identified methods of increasing herbage availability in spring, but little focus was placed on how this impacts animal production. The aim of the current study was to investigate the impact of opening farm cover (OFC; grass availability on farm at turnout in spring; 1036 (high), 748 (medium) and 544 (low) kg DM/ha) and spring rotation length (fast – 56 days and normal – 63 days) on animal performance in early lactation and herbage production and quality. Spring rotation length had little effect on animal performance, herbage variables or sward composition. High OFC increased pre-grazing herbage mass, allowing for increased daily herbage allowance (DHA) compared to medium and low OFC. There was a reduced proportion of leaf in the sward of the high OFC compared to the low OFC, resulting in lower organic matter digestibility. Despite the reduction in sward quality observed as a consequence of achieving high OFC in spring, the greater DHA available to animals increased milk production (+1.4 kg milk/cow/day). Additionally, animals grazing a medium or low OFC had a greater requirement for silage supplementation in spring (+1.3 kg DM/cow/day). The benefits of the higher DHA highlighted in the current study suggest that autumn grazing management must be adapted to increase herbage availability in spring. However, the benefits observed in milk production did not persist beyond the first grazing rotation.

White clover (Trifolium repens L.; clover) can offer a superior nutritional feed compared with perennial ryegrass (Lolium perenne L.; PRG) and offers an additional or alternative source (or both) of N for herbage production. The objective of this study was to investigate the effect of including clover into PRG swards receiving 150 (Cl150) or 250 kg of N/ha (Cl250) compared with a PRG-only sward receiving 250 kg of N/ha (Gr250) on herbage production, milk production, and herbage dry matter intake (DMI) in an intensive grass-based spring calving milk production system over 2 full lactations. A farm systems experiment was established in February 2013, and conducted over 2 grazing seasons [2013 (yr 1) and 2014 (yr 2)]. In February 2013 (yr 1), 42 Holstein-Friesian spring-calving dairy cows, and in February 2014 (yr 2), 57 Holstein-Friesian spring-calving dairy cows were allocated to graze the Cl150, Cl250, and Gr250 swards (n = 14 in yr 1 and n = 19 in yr 2) from February to November, at a stocking rate of 2.74 cows/ha. Herbage DMI was estimated twice in yr 1 (May and September) and 3 times in yr 2 (May, July, and September). Treatment did not have a significant effect on annual herbage production. Sward clover content was greater on the Cl150 treatment than the Cl250 treatment. The cows grazing both clover treatments (Cl250 and Cl150) produced more milk than the cows grazing Gr250 from June until the end of the grazing season. A significant treatment by measurement period interaction was observed on total DMI. In May, the cows on the Cl250 treatment had the greatest DMI. In July, the cows on the clover treatments had greater DMI than those on the Gr250 treatment, whereas in September, the cows on the Cl150 treatment had the lowest DMI. In conclusion, including clover in a PRG sward grazed by spring-calving dairy cows can result in increased animal performance, particularly in the second half of lactation. Reducing N fertilizer application to 150 kg of N/ha on grass-clover swards did not reduce herbage production compared with grass-only swards receiving 250 kg of N/ha. White clover can play an integral role in intensive grazing systems in terms of animal performance and herbage production.

Abstract A 4-year (2010–2013) plot study was undertaken to evaluate the effect of nitrogen (N) fertilizer rate (0, 60, 120, 196 and 240 kg N/ha/year) on seasonal responses and species persistency in frequently and tightly grazed (⩽4 cm) grass-only (GO) and grass white clover swards (GWc). Increasing N application rate increased herbage removed and pre-grazing sward height. Cows frequently grazed the GWc tighter than the GO. Increasing N rate reduced clover content, especially during the warmest months of the year, but less so up to 120 kg N/ha/year. The GWc had greater amounts of herbage removed than GO in the May–September period but the effect was less as N rate increased. Cumulative herbage removed from GWc was greater than GO swards receiving the same N rate and herbage quality was better in GWc than GO. Such effects were reduced as swards aged and with increasing N rate. It was concluded that under frequent and tight grazing management: (1) clover inclusion increased annual herbage removed; (2) herbage removed from GWc swards receiving no N was the same as the GO sward receiving 240 kg N/ha, and greater for the 240 GWc swards than the 240 GO swards; (3) clover inclusion benefits were mainly from summer onwards; (4) the management strategy applied in the current experiment may be capable of alleviating the detrimental effect of N fertilizer on clover, to a point between 60 and 120 kg N/ha.

SUMMARY The current experiment was undertaken to investigate the effect of including white clover (Trifolium repens L.; WC) into perennial ryegrass (Lolium perenne L.; PRG) swards (PRG/WC) receiving 250 kg nitrogen (N) per hectare (ha) per year compared with PRG only swards receiving 250 kg N/ha/year, in an intensive grass-based spring calving dairy production scenario. Forty spring-calving cows were allocated to graze either a PRG/WC or PRG sward (n = 20) from 6 February to 31 October 2012. Fresh herbage was offered daily (17 kg dry matter (DM)/cow) supplemented with concentrate in times of herbage deficit (total supplementation 507 kg/cow). Pre-grazing herbage mass (HM), sward WC content and milk production were measured for the duration of the experiment. Herbage DM intake was estimated in May, July and September. Pre-grazing HM (±s.e.) was similar (1467 ± 173·1 kg DM/ha) for both treatments, as was cumulative herbage production (14 158 ± 769 kg DM/ha). Average WC content of the PRG/WC swards was 236 ± 30 g/kg DM. The PRG/WC cows had greater average daily milk yield and milk solids yield from June onwards. Cumulative milk yield and milk solids yield were greater for the PRG/WC cows compared with the PRG cows (5048 and 4789 ± 34·3 kg milk yield/cow, and 400 and 388 ± 1·87 kg milk solids/cow, respectively). Cows had similar DM intake in all measurements periods (15·1 ± 0·42 kg DM/cow/day). In conclusion, including WC in N-fertilized PRG swards increased milk production from cows grazing the PRG/WC swards compared with PRG, particularly in the second half of the lactation.